Man page 9 : skb_pull

skb_pull - remove data from the start of a buffer

unsigned char * skb_pull(struct sk_buff *  skb , unsigned int  len );

skb
    buffer to use

len
    amount of data to remove

This function removes data from the start of a buffer, returning the memory to the headroom. A pointer to the next data in the buffer is returned. Once the data has been pulled future pushes will overwrite the old data.